1. Field of the Invention
The present invention relates to a disk drive, and more particularly to a disk drive utilizing a magnetic disk medium of a DTR structure.
2. Description of the Related Art
Attention has recently been paid to a magnetic disk medium (hereinafter referred to simply as “the disk medium”) as a patterned medium of a discrete track recording (DTR).
The disk medium of the DTR structure comprises a first surface section effective as a magnetic recording section, and a second surface section ineffective as the magnetic recording section (see, for example, Jpn. Pat. Apple. KOKAI Publication No. 8-293110). The first surface section is a projected magnetic region on which a magnetic film is provided. The second surface section is a non-magnetic region or depressed magnetic-recording-incapable region. Namely, the second section, which is a depressed section, is configured as substantially a non-magnetic region even if a magnetic film is provided thereon.
In this type of disk medium, servo regions with servo data recorded therein can be embedded in the surface of the medium, without using a standard servo track writer.
The servo data contains, as well as sector address data and track address data, servo pattern data for detecting a positional error in a track (this may hereinafter be referred to as error detection servo pattern). The error detection servo pattern includes a servo pattern called a null servo pattern, as well as a burst servo pattern (see, for example, PCT National Publication No. 2002-516450).
The null servo pattern enables the formatting efficiency of each sector on a disk medium to be improved, and enables the total area of the servo regions on the medium to be reduced. The null servo pattern contains a synchronization region and a positional error region, and can acquire, using an asynchronous digital decoder, a positional error signal without being synchronized with a read signal.
The null servo pattern is written on a disk medium by a servo track writer. On the other hand, in disks of the DTR structure, conventional burst servo patterns are generally embedded.
In disks of the DTR structure, however, it is not easy to embed servo patterns in a disk by a transfer forming method, since the ratio of the entire area of the data regions to that of the servo patterns is high. More specifically, it is difficult to apply uniform pressure during a transfer forming process and hence to form uniform servo patterns. As a result, the accuracy of head positioning using the resultant servo patterns may well be degraded.